Titanium-aluminium alloys and inter-metallic compounds (generically termed herein “titanium-aluminium compounds”) are very valuable materials. However, they are difficult and expensive to prepare, particularly in the preferred powder form. This expense of preparation limits wide use of these materials, even though they have highly desirable properties for use in automotive, aerospace and other industries.
Titanium minerals are found in nature in the form of a very stable oxide (TiO2). Common processes for the production of titanium are the Kroll process and the Hunter process. The Kroll process requires the use of magnesium as a reducing agent to reduce TiCl4 (prepared from the oxide by a pre-process of chlorination) to produce the Ti metal. The Hunter process requires the use of sodium as the reducing agent. Because TiCl4 is still thermodynamically stable, highly reactive reducing agents such as magnesium or sodium are required to produce titanium metal out of TiCl4. Such highly reactive reducing agents are difficult and expensive to handle. As the magnesium chlorides in the case of the Kroll process are stable up to temperatures in excess of 1300K, the product is often in the form of a Ti sponge mixed with MgCl2 and remnants of Mg and TiCl2. To obtain pure Ti, the product requires extensive post-processing, including washing and melting in a vacuum arc furnace to remove all impurities. This contributes to the present high cost of the production of titanium.
In the known technologies for production of titanium alloys such as Ti—Al—V, and intermetallic compounds such as Ti3Al, TiAl, TiAl3, Ti—Al—(Cr, Nb, Mo, etc) and alloys based on these compounds, appropriate amounts of sponges, ingots or powders of the metals which comprise these alloys are milled or melted together and annealed, hence adding to the production cost, particularly as it is necessary to obtain the metals first which, as discussed, in the case of titanium, involves considerable expense. For production of a powder of these titanium alloys and intermetallic compounds, further processing is usually required, adding to the already high production cost.
Over the past several decades, there have been extensive attempts made to replace the existing Kroll and Hunter technologies using techniques such as electrowinning, plasma-hydrogen and also aluminothermic reduction. In attempts to perform direct reduction of TiCl4 with aluminium, an uncontrollable production of product compounds of widely different composition occurs, for instance intermetallic compounds such as Ti3Al, TiAl, TiAl3. Because of the difficulties associated with uncontrollable gas phase reactions it has not been possible to achieve the production of a single phase material of titanium and/or titanium-aluminium compounds by direct reduction of titanium chlorides.